Formation of polycrystalline semiconductor material has been extensively studied over the years.
Conventional ways of making polycrystalline silicon (poly-Si) are, for example, low-pressure chemical vapour deposition (CVD) and solid-phase recrystallization by thermal annealing. These methods require or a high-temperature (higher than 600° C.) deposition or thermal annealing for a long time.
Another way of forming poly-Si is by performing recrystallization using laser annealing. Such a method is described by Do Young Kim et al. in “Ultra-low temperature poly-Si thin film transistor for plastic substrate”, Journal of the Korean Physical Society, vol. 48, 2006, pp. S6-S63. In this method, an amorphous silicon (a-Si) film is provided on a substrate by using RF (radio frequency) sputtering at 200 W with an Ar or Xe plasma and at room temperature. The a-Si film is then crystallised by ELA (eximer laser annealing) by using a XeCl laser, for example with post-annealing during 2 hours at 200° C.
The method described by Do young Kim et al. is time consuming and consequently also expensive. Furthermore, laser annealing requires subtle adjustment of spot size and the intensity of laser beams to prepare homogenous poly-Si films.